1. Field of the Invention
The invention pertains to the field of mechanical engineering and construction as well as to conveyor and processing technology. It relates to a device and a method for generating a controllable reciprocal movement of a moveable mechanical element. The invention is particularly applicable as a singling device for the controllable separation of items from a stack. The items are for example print shop products that are pushed out of a stack of print shop products.
2. Description of Related Art
A shuttle feeder for tabular material is disclosed in DE-A 33 20491. The respective lower item of an item stack is pushed out of the stack by a separation element in such a way that it can be accepted by conveyor belts of an outgoing conveyance device and transported away. The separation element is mounted such that it is linearly moveable and coupled to a driveshaft via an articulation system. The continual rotary motion of the drive shaft is, thus, converted to a linear reciprocal movement of the mechanical element between two stop positions. With this known system one item is pushed out of the stack per rotation of the drive shaft. If one would like to interrupt the removal of items, the drive must be stopped.
In printing technology in particular, but also in other areas of use, it is necessary to select single items on demand, and at precisely timed intervals. In the area of production of newspapers and magazines it is increasingly desired that the main products, e.g. the actual newspaper and/or magazine can be furnished individually with one or more supplements. The supplements are, for example, advertising brochures, flyers, samples, CDs and the like. They can comprise a thickness of 3 mm and more and be rigid, whereby known singling devices, which bend the items during separation, cannot be used. The items are made available in a stack. It is thus necessary to separate these items from the stack in a targeted and temporally precise manner. For this reason the high production cycle of up to 30,000 products per hour should be maintained. At these rates, it is out of the question to turn the drive motors of the singling device and/or the separation element on and off.
Thus another known solution is to couple the separation element by means of a controllable coupling to a continually running drive in order to achieve on-demand separation of an item. In this case the rotary motion of the driveshaft is converted by means of a converter, for example an eccentrically-mounted piston rod, into a reciprocal movement of a drive element, e.g. a piston. The separation element can be coupled to the drive element via a coupling, whereby in a coupled state it is taken along and also describes a reciprocal movement. To prevent rapid deterioration, the coupling must be closed in an unloaded state. The unloaded state exists only at the turning points or turning positions, respectively, of the reciprocal movement of the drive element. The ideal time window for connection is thus very small, whereby either the coupling must be connected under load or the pulse frequency must be limited.